Amplifier



Feb. 23, 1943' H, RQDER 2,312,194

AMPLIFIER Filed ma 28, 1941 Fig- 8 I 10 =2 7 I 1/ 12 i f g 35 E n T v 13Q! I m z Q a it k Q Q LL! (I) Q (n V) Q 0 E2 5 3 E .3 w k D i a v f 1FREQUENCY- a I z a v 4 ACTIVE ACTIVE Pawm POWER Mm PLATE BASIS/H4770AAAAAA Vvvvv INVENTOR HANS R0052 BfWZ ' ATTORNEY Patented Feb. 23, 1943AMPLIFIER Hans Roder, Berlin, Germany; vested in the Alien PropertyCustodian Application May 28, 1941, Serial No. 395,581

In Germany January 31, 1940- Claims. (Cl. 179-171) A requirementfrequently arising in radio intelligence transmission is to transmit notonly a dellnite radio frequency but it is occasionally demanded thatwithin a certain range or banda change of Wave length should be possiblewithout the incidental necessity of retuning the various stages of thesending or receiving signal am- It is known in the art of theseamplifiers t0 differently tune the oscillatory circuits of the variousstages in respect to one another and to introduce, where necessary,additional damping. The band width thus obtainable is comparativelylimited if the efiiciency of the gain is to stay high.

It is also known in the prior art to intercouple the sequential stagesof a radio frequency amplifier by net-works or filters, thelatter'having a band-pass commensurate to the wave band within which thetransmission efliciency is to be uniform. This circuit organization hasthe drawback that it is very difficult to obtain a uniform efficiencyover the desired tuning range, especially where.

transmitter amplifiers are operated as class C amplifiers. Over anyconsiderable band width, undesirable harmonics are also transmitted.

The invention obviates these difficulties. The invention is predicatedupon the consideration hereinafter to be outlined and which may be.

taken into consideration, for instance, in connection with the load ofthe power stage of a transmitter amplifier in conjunction with a tuneddamped antenna.

The power stage, when it is resonant, has as its only load the ohmicresistance of the antenna. In other words, a pure ohmic or active loadis involved, while in the absence of resonance-capacitive or inductivereactance powers are involved, and these must be introduced in theoscillation circuit from the outside in order that a. constant potentialmay be maintained in the circuit.

Now, if care is taken so that when a wattless current is wanted in acertain part of the circuit, corresponding wattless currents of oppositesign the frequency deviates from the resonance frequency of the tunedload are compensated by wattless currents of opposite sign supplied froma tube.

A more detailed description follows, wherein Figure 1 shows a preferredcircuit arrangement embodying the invention;

Fig. 2 is a graphic representation of a certainfrequency responsecharacteristic;

Fig. 3 shows graphically a coordination between the wattless power andthe plate dissipation observed in the operation of a certain dischargetube of my system; and

Fig. 4 shows a modified circuit arrangement for carrying out theinvention.

Referring to Fig. 1, the potential E arising across the input terminalsI and 2 is impressed through voltage divider 3 and lead 4 upon thecontrol grid 5 of pentode 6. Included in the output circuit of the tube6 isthe load 1 represented in the form of an oscillatory circuitcomprising a paralleled ohmic resistance, said load being, for instance,an antenna of around 25 to 30 percent damping. If the plate alternatingpotential is practically constant in the presence of variations offrequency, then the current which flows I through this circuit has ashape as shown graphi- I cally in Fig. 2 where the plate alternatingcurrent Ia is plotted as a function of the frequency f. In the presenceof resonance frequency fl. current In has a good power factor. But upondeparture from the resonance frequency either upwards or downwards, theplate a. 0. will be increased as a result of the production ofcapacitive or inductive wattless currents.

However, it will be understood that the plate alternating potential canbe stabilized only if the wattless current arising upon the departurefrom the resonance frequency is supplied from the outside. For in thismanner conditions can be made so that not only for the resonancefrequency, but rather for a comparatively broad band, there is, as itwere, permanently a purely resistive load, with the consequence that thepower factor remains constant even in the presence of frequencyvariations. This condition as shown, for example, in Fig. 1 isattainable by connecting in parallel relation to the main amplifierchannel 8, 9 a tube it) which is so controlled that it will furnish thewattless current required for compensation. Tube Ill receives itscontrol potential by way of a condenser I l and a resistance I2 causingthe requisite phase shift, from one and the same voltage di- 'vider 3,the latter supplying also the potential for the tube In parallelrelation to the grid cathode path is arranged a voltage resonancecircuit it which comprises the capacity. II and the v a wattlesscomponent designed to compensate the wattless component of circuit 1.The com-' pensatory action and thus the band-width are restricted byvirtue of the fact that below the resonance frequency current resonanceis conditioned by capacitor H and inductance l8, while above theresonance frequency the choke-coil I! and the capacitor l'l form afurther current resonance point beyond which-always figured and viewedfrom the resonance point of circuit ll-the control potential thus farrising is caused again to decline speedily.

In order to make sure that the wattless current furnished from tube IIIwill be always proportional to the potential drop in circuit l3, it isimperative that tube l should operate within a certain limited range ofclass A, class B, and class C amplification, because of the variabilityof the grid potential. Tube 6, as will be understood, should work as aclass C amplifier for the sake of improved efllciency, as is customaryin amplifiers forming a part of transmitters.

Now, it has been ascertained that the provision of a tube designed tosupply additionally the wattless current is not always necessary. On thecontrary, the main amplifier may be relied upon to furnish the wattlesspower. This discovery was made only after exhaustive research andcalculations the findings of which will be further explained. Theconditions such as they are, may be described by reference to a pentode,which is particularly suited to the circuit under discussion, becausethe reaction of the plate upon the grid is practically absent, due tothe limited value of the grid plate capacitance and the small influenceof the plate voltage upon the plate current.

Fig. 3 shows what active and reactive or wattless powers may be securedfrom a pentode for different plate D. C. voltages. The assumption ishere made that the plate dissipation of the tube is stabilized; to bemore precise, that it is equal to the maximum admissible value. Anotherpresupposition is that the plate alternating potential is driven alwaysclose to the limit between under-volted and over-volted operation. ofcourse; to the various points of the curve correspond load impedancesthe size and phase of which are given by the straight line from theorigin to the points of the curve. Plotted on the abscissae is theactive yield," in other words, the ratio of active power to platedissipation, and on the ordinates the reactive yield"; that is to say,the ratio of wattless power to plate dissipation, the parameters beingthe plate D. C. voltage, though the values indicated alongside thegraphs are merely relative figures or proportional numbers. The furtherassumption is made that the current fiow angle is constant and that itamounts to 60 degrees. angle, by definition, indicates what angularproportion of the entire control potential is co- ThiS ordinated to therange in which plate current flows. In order to simplify thecalculations it is customary to designate one-half of this angularproportion as the current flow angle. For instance, in the case of classA amplifier operation, the said angle amounts to 180 degrees; for pureclass B operation, it is degrees, and for C operation correspondinglyless.

With due regard for the efficiency in the case of resonance, the tubeworks also under conditions of class C operation. In thecase of thecircuit organization shown in Fig. l where the tube l0 furnishing thewattless current could not be operated satisfactorily as a class Camplifier, particularly due to the variable grid voltages. Hence it wasat first thought that difiicuities would be encountered in obtaining thesimultaneous delivery of active and wattless current as output from asingle tube, especially when operated as a class C amplifier. However,it has been discovered that such operation is entirely feasible.

In the first place this surprising fact is found that for cos 4 =0 thewattless power is practically independent of the plate D. C. voltage,and that, moreover. it is appreciably lower than the maximum watt oractive power. But if from one and the same tube watt and wattless powerbe .taken simultaneously, it is found that the wattless component of thetube becomes considerably higher than in the case of purely wattlessoperation. For instance, for parameter 14 the wattless yield in thepresence of =90 degrees is only .91; for =39 degrees, it is =l.6, whilethe active power yield becomes equal to 2. In other words, maximumwattless yield is secured in a tube, if at the same time a wattcomponent of roughly the same value is taken off.

The graphs Fig. 3 show that a comparatively large watt and wattlesscomponent is simultaneousiyderivable from the tube without the platedissipation of the tube being made excessive. However, these findingssuggest that the elimination of the additional or separate tube tofurnish the wattless component shown in the circuit scheme Fig. 1, andfurthermore the main tube may be depended upon for the supply of thewattless component as shown, for instance, in Fig. 4. This main tube 20(Fig. 4) corresponds with tube 6 in Fig. 1. It feeds to a load orconsumer, say a more or less damped aerial. The damping can be producedby a parallel oscillation circuit 2| with paralleled resistance 28. Tube20 receives its control potential from an input tube 22 whichpractically works with a constant input potential.

The grid circuit of tube 20. similarly as in the case of tube I0, Fig.1, contains a voltage resonance circuit 23 in series with a resistance26 in parallel relation to the grid-filament path or circuit which istuned to the same frequency as the oscillatory circuit 2| in the outputcircuit of tube 20. The grid leak choke-coil is indicated at 24, whilethe input and circuit capacities represented by dash-lines are indicatedat 25. In the presence of a state of resonance the control grid 21 oftube 20 is only impressed with the potential arising across theresistance 26.

In the case of departures'from the resonance point the wattlesspotential occurring in the potential resonance circuit has the resultthat the tube will furnish wattless current in addition to the active orwatt current, and this wattless or idle current will supply and-coverthe wattless current requirements of the consumer or load to a pointsuch that the same will function like a purely resistive load. Theresonance circuits must be so proportioned that a relatively broad bandis transmitted at uniform efliciency, say, a range of one octave.

The circuit organizationsv shown, byway of example, in the appendeddrawing comprise pentodes, though it will be evident that it is alsopossible to use triodes, if care be taken that the reaction caused bythe plate upon the grid is practically compensated, say, by means ofneutralizing circuits.

I claim:

1. A radio frequency amplifier circuit adapted to transmit a definitefrequency of a frequency band covering at least an octave, said circuithaving a discharge tube in combination with means including an auxiliarydischarge tube whereby the wattless currents arising in the case ofdeparture of the frequency from the resonance frequency of a tuned loaddevice are compensated by wattless currents of opposite sign furnishedby said tube.

2. A circuit according to claim 1, wherein the grid circuit of theauxiliary tube contains the seriation of an ohmic resistance and avoltage resonancecircuit tuned to the same frequency as the load device,the same being so proportioned that the wattless currents required forcompensation are furnished by the tube.

3. In a radio frequency amplifier, an electron discharge tube havinginput and.output circuits, 9. load in said output circuit, said loadbeing receptive to a band of frequencies covering at least one octaveand being resonant at a frequency within said band, the inductive andcapacitive values of said load being adjusted to develop predeterminedvalues of wattless current components at different frequencies withinsaid band, and means including an auxiliary discharge tube for providingcompensation with respect to said wattless current components such thata substantially uniform power factor is obtained throughout said band.

4. The combination according to claim 3 and including in parallel withsaid discharge tube a second discharge tube having an input circuit atleast a portion of which is common to the afore mentioned input circuit,and resonant means for feeding the control potential to the first saiddischarge tube, said resonant means being connected to an intermediatepoint on a voltage divider across the leads from a source of controlpotentials, and said second discharge tube being controlled by arelatively larger value of said control potentials.

5. An amplifier circuit arrangement in com- .bination with a load havinga substantially pure conductance at a predetermined frequency alsohaving a capacitive susceptance above said frequency and an inductivesusceptance below said frequency, means for automatically neutralizingthe susceptance components comprising a variable impedance in shunt withsaid load, said means comprising a discharge tube the space path ofwhich is in shunt relation to said load and the input circuit of whichis energized from an input voltage common to that of said amplifier, butdiffering in phase therefrom, and means including a series resonantcircuit in shunt with a portion of said input circuit for disabling saidtube when said predetermined frequency is delivered by said amplifier tosaid load.

HANS RODER.

